The Growing Point | July 2020
Scouting for fusarium head blight infection post fungicide application
After cereal head fungicide application is complete, fusarium head blight (FHB) monitoring is not over. The next step is to scout your crop 10-14 days after anthesis for FHB infection symptoms. Scouting post-anthesis can give you a better idea of FHB field infection and allow you to better plan for harvest as well as make stronger management decisions for the following year’s crop.
When scouting for FHB in wheat, you are mainly looking for premature bleaching of infected spikelets (Figure 1) as well as pinkish-orange, spore-bearing structures at the base of the glumes (Figure 2). Premature bleaching can occur in all spikes on the head, or just some, depending on which flowers were infected during anthesis. If weather is damp, you may witness pinkish, fluffy fungal growth. Additionally, in wheat, the rachis (the part of the stem between the kernels that the kernels are attached to) and the top part of the stem may display a honey brown discolouration.
Figure 1: Visual symptoms of fusarium head blight in wheat (Image: Dr. Kelly Turkington AAFC Lacombe; photo taken from Dr. Maria Antonia Henriquez’s FHB screening nursery, AAFC Morden, 2019).
Figure 2: A fusarium-infected wheat head displaying orange, spore-bearing structures at the in the crevices and at the base of the glumes (Image: Dr. Kelly Turkington AAFC Lacombe)
Symptoms of FHB in wheat are fairly distinct from other plant diseases including stagnospora glume blotch (SGB), which rather than producing bleach heads or portions of heads with organish-pinkish sporulation, results in brownish to brownish purple lesions that are dotted with small bumps (pycnidia) which are fruiting structures that release rain-splashed pycnidiospores Figure 3).
Figure 3: Stagnospora glume blotch in a wheat head (Image: Dr. Kelly Turkington AAFC Lacombe)
Wheat kernels impacted by SGB can be mistaken for fusarium damaged kernels (FDK) during grading. For this reason, if downgrading occurs due to FDK with zero to limited history of FHB in your fields or region, it would be valuable to test your grain at an accredited lab to ensure that FHB pathogens are indeed present.
Stripe rust can also cause premature ripening of portions of the wheat head resembling FHB when rust infection is substantial and occurs on the head (Figure 4). With stripe rust, however, you can often see the appearance of the uredospores on, or within infected florets, and they tend to have an bright orangish yellow granular appearance.
Figure 4: Stripe rust in found in wheat head glume (Image: Dr. Kelly Turkington AAFC Lacombe)
For barley, identification of FHB is more challenging as symptoms are less obvious (figure 5) and can be easily confused with head infections caused by spot blotch or net blotch pathogens. If conditions are moist you may see the appearance of whitish-pink hyphae and pinkish-orange sporulation, but the infected tissue itself will typically be brownish in colour. It’s advisable to submit suspect plant material to a lab for testing.
Figure 5: Fusarium infected barley head (Image: Dr. Kelly Turkington AAFC Lacombe)
If, through scouting and lab testing, you determine you have FHB infection in your crop, steps can now be taken prior to and during harvest to mitigate its impact. This following list is not exhaustive. For full details on harvest and post-harvest management of FHB, please visit our new site, Let's Manage It! at managefhb.ca.
First, you can assess other fields to determine if they carry the same level infection. Fields that flowered at different times may not have the same infection level. If you find this is the case, storage separation of infected and non-infected fields may be an option. By storing infected and non-infected grain separately, you are better able to market and manage each crop.
Knowledge of field infection helps determine if you should adjust your combine settings during harvest to blow lightweight FDK out of the grain. Keep in mind, these infected kernels are one of the most highly prolific producers of the wind-borne stage of the FHB pathogen. Spreading the FDK back onto the field further inoculates your soil. The alternative option is to maintain the FDK for post-harvest cleaning later in a gravity or colour sorter.
In planning for the next season, you can then be more cautious with what grain may be utilized for seed. Suspect grain, or grain that has been verified to contain Fusarium graminearum through testing can be treated with a seed treatment, or, a different seed lot could be used all together. This is especially important for regions where FHB field inoculum is low and avoiding the seeding of FHB infected seed may help maintain low inoculum levels. If you have no other seed options that a free from infection, ensure you are treating suspect grain or grain with confirmed infection with a seed treatment. Using infected grain should be a last resort.
All of these tactics can help mitigate the effects FHB has on your farm. Scouting post-anthesis will help you be better prepared to enlist them.